<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .box {
        width: 500px;
        height: 400px;
        border: 1px solid #000;
        position: relative;
        margin: auto;
        overflow: hidden;
        cursor: pointer;
    }

    .box ul,
    .box ol {
        list-style: none;
        padding: 0;
        margin: 0;
    }

    .box ul li {
        width: 500px;
        height: 400px;
        display: none;
    }

    .box ul li img {
        width: 500px;
        height: 400px;
    }

    .box ol {
        width: 120px;
        position: absolute;
        left: 50%;
        margin-left: -40px;
        bottom: 20px;
        height: 20px;
        background: rgba(255, 255, 255, 0.482);
        display: flex;
        justify-content: space-evenly;
        padding: 10px 0;
        border-radius: 20px;
    }

    .box ol li {
        width: 20px;
        height: 20px;
        border-radius: 50%;
        background: pink;
        border: 1px solid #999;
    }

    .box ol li.current {
        background: red;
    }

    .box ul li.current {
        display: block;
    }

    .box .left,
    .box .right {
        position: absolute;
        top: 50%;
        width: 30px;
        height: 30px;
        margin-top: -15px;
        background: #ccc;
        text-align: center;
        line-height: 30px;
        text-decoration: none;
        font-weight: bold;
        color: #fff;
    }

    .left {
        left: 0;
    }

    .right {
        right: 0;
    }
</style>

<body>
    <div class="box">
        <ul>
            <li class="current"><img src="images/1.jpg" alt=""></li>
            <li><img src="images/2.jpg" alt=""></li>
            <li><img src="images/3.jpg" alt=""></li>
            <li>
                <img src="images/4.jpg" alt=""></li>
        </ul>
        <ol>
            <li class="current"></li>
            <li></li>
            <li></li>
            <li></li>
        </ol>
        <a href="javascript:;" class="left">&lt;</a>
        <a href="javascript:;" class="right">&gt;</a>
    </div>
</body>
<script type="text/javascript">
    /*
        实现功能
        1、自动切换图片 保证小圆点跟随
        2、上一张下一张点击切换图片  小圆点也需要跟随
        3、点击小圆点 切换到对应的图片
    */ 

    // 保存定时器标识
    var timer;
    var i=0
    var lefts = document.querySelectorAll('.ul>li');
    var rights= document.querySelectorAll('.ol>li');

    function play(){
        timer = setInterval(function(){
document.querySelector('ul>.current').className=''
lefts[i].className='current'
document.querySelector('ol>.current').className=''
rights[i].className='current'
i++
if(i==lefts.length){
i=0
}
        },1000);
    }

var aaa= document.querySelector('.right')       
 aaa.onclick=function(){
rights.forEach(function(sum){
   this.className=aaa[sum]
})
}

   document.querySelectorAll('ol>li').forEach(function(max,min){
    max.onclick=function(){
        document.querySelector('ol>.current').className=''
        this.className='current'
        
    }
   })
   
   document.querySelectorAll('ol>li').forEach(function(dom){
            dom.onclick = function(){
          
                document.querySelector('ol>img').src = this.href;
          
                document.querySelector('ol>.current').innerHTML = this.getAttribute('ul>.current')
         
                return false;
            }
        })
</script>

</html>